The present invention relates to a display device, such as a liquid crystal display device, and a method for manufacturing the same, and more particularly to a cutting method for cutting a glass substrate constituting a liquid crystal display device.
In general, a liquid crystal display device is manufactured as follows.
Two glass substrates each having electrodes are prepared. Spacers are provided on the overall surface of one of the glass substrates to keep the distance between the substrates constant when they are adhered to each other. The spacers are fixed to predetermined positions of the substrate by, for example, the photolithography process. The spacers are arranged uniformly in a display area, i.e., an area surrounded by sealing material applied in a subsequent process. In a peripheral area, outside the display area, the spacers are arranged uniformly at a density lower than that in the display area. A sealing material is applied to one of the glass substrates, the two substrates are adhered to each other, and then the sealing material is cured. The two glass substrates are cut into a desired size, and a liquid crystal material is sealed between the two substrates, thus forming a liquid crystal display device.
The dicing and piezoelectrical methods are known as methods for cutting glass substrates. Of the methods, the scribing method is most generally employed. Glass substrates are cut by the scribing method in the following manner.
A predetermined cut line is scribed on a surface of a glass substrate by a scriber made of a hard material, such as sharp-edged diamond, thereby forming a crack along the cut line. The crack is extended by shock applied on the other surface of the glass substrate on which the crack is not formed, so that the glass substrate can be cut.
To cut a glass substrate of a liquid crystal display device, a cut line on a surface of the glass substrate is scribed, thereby forming a crack, i.e., a scribe line, along the cut line. A shock is given uniformly to the glass substrate by a rod-like member made of rubber, called a brake bar, along the scribe line from the other surface of the glass substrate. As a result, the glass substrate is broken along the scribe line, so that it can be cut into a desired size.
In the steps of manufacturing a liquid crystal display device, first and second glass substrates adhered to each other via spacers are cut in the following manner. The spacers are fixedly formed on predetermined positions of the second glass substrate.
A scribe line is formed on a surface of the first glass substrate. A shock is uniformly given along the scribe line by a brake bar to a surface of the second glass substrate opposing to the first glass surface, thereby cutting the first glass substrate.
At this time, since there are only spacers between the two glass substrates, the shock given by the brake bar is transmitted from the second glass substrate to the first glass substrate through the spacers. For this reason, the shock is concentrated on the spacers, and the crack formed by the scriber is liable to extend toward the spacers by the shock. Therefore, the shape of a cross section of the glass substrates after cutting is related very closely to the positions of the spacers.
In the peripheral area, since the spacers are arranged in portions separated from the scribe line at a comparatively lower density, the crack may extend toward the spacers. Therefore, the cut surface of the glass substrates is not substantially perpendicular to the main surface of the substrate, but a sharp, irregular cross section is formed. Thus, the aforementioned arrangement of the spacers raises problems such as a high possibility of cut defects and a low manufacturing yield. The cut defects may easily cause a glass crack in the subsequent manufacturing steps. A piece of cracked glass may enter a gap between the glass substrates or between a glass substrate and a polarizing plate; that is, a so-called "fragment jam defect" may occur.
In general, the position at which the brake bar applies a shock to a glass substrate (the brake position) may probably be shifted by about 1 mm from the scribe line. If a shock is given to the glass substrate with the brake bar shifted from the scribe line, the shock may be transmitted to spacers located apart from the scribe line. In this case, a number of cut defects may be generated, producing glass cracks or fragments, with the result that the manufacturing yield is lowered.
Further, in most liquid crystal display devices, an array substrate has a plurality of driving circuits in the peripheral area. In particular, a number of wiring patterns are formed around the scribe line. If a spacer is placed on a wiring pattern, the height of the spacer is greater than that of another spacer located on the glass substrate by the thickness of the wiring pattern. Therefore, the shock given by the brake bar is not uniformly transmitted to all the spacers, but concentrated on the spacers on the wiring patterns. In this case, cut defects may easily occur and the wiring pattern may be damaged by the shock, with the result that the manufacturing yield is lowered.
As described above, the structure wherein spacers are arranged at a comparatively low density in positions apart from the scribe line has the following problems. When the glass substrate is cut, cut defects are liable to occur depending on the positions of the spacers, the shift of the brake position with respect to the scribe line, and the positional relationship between the spacer and the wiring pattern. If the cut defects occur, glass cracks or fragments may be produced in the subsequent steps, resulting in a low manufacturing yield.